Coated article with low-e coating including zirconium oxide and/or zirconium silicon oxynitride and methods of making same

ABSTRACT

This application relates to a coated article including at least one infrared (IR) reflecting layer of a material such as silver or the like in a low-E coating. In certain embodiments, at least one layer of the coating is of or includes zirconium oxide (e.g., ZrO 2 ) or zirconium silicon oxynitride (e.g., ZrSiO x N y ). When a layer comprising zirconium oxide or zirconium silicon oxynitride is provided as the uppermost or overcoat layer of the coated article (e.g., over a silicon nitride based layer), this results in improved chemical and heat stability in certain example embodiments. Coated articles herein may be used in the context of insulating glass (IG) window units, vehicle windows, or in other suitable applications such as monolithic window applications, laminated windows, and/or the like.

This application relates to a coated article including at least oneinfrared (IR) reflecting layer of a material such as silver or the likein a low-E coating. In certain embodiments, at least one layer of thecoating is of or includes zirconium oxide (e.g., ZrO₂), zirconiumoxynitride, or zirconium silicon oxynitride (e.g., ZrSiO_(x)N_(y)). Incertain example embodiments, the provision of a layer comprisingzirconium oxide or zirconium silicon oxynitride permits a layer to beused which has a high refractive index and ultraviolet (UV) absorption.When a layer comprising zirconium oxide or zirconium silicon oxynitrideis provided as the uppermost or overcoat layer of the coated article(e.g., over a silicon nitride based layer), this results in improvedchemical and heat stability in certain example embodiments. Thus, incertain example embodiments, UV absorption for example may be improvedif desired. Coated articles herein may be used in the context ofinsulating glass (IG) window units, vehicle windows, or in othersuitable applications such as monolithic window applications, laminatedwindows, and/or the like.

BACKGROUND AND SUMMARY OF EXAMPLE EMBODIMENTS OF THE INVENTION

Coated articles are known in the art for use in window applications suchas insulating glass (IG) window units, vehicle windows, monolithicwindows, and/or the like. In certain example instances, designers ofcoated articles often strive for a combination of high visibletransmission, low emissivity (or low emittance), and/or low sheetresistance (R_(S)). High visible transmission may permit coated articlesto be used in applications where these characteristics are desired suchas in architectural or vehicle window applications, whereaslow-emissivity (low-E), and low sheet resistance characteristics permitsuch coated articles to block significant amounts of IR radiation so asto reduce for example undesirable heating of vehicle or buildinginteriors. Thus, typically, for coatings used on architectural glass toblock significant amounts of IR radiation, high transmission in thevisible spectrum is often desired. However, low transmittance and/orhigh reflectance in the IR and/or near IR part(s) of the spectrum isalso desired to reduce for example undesirable heating of vehicle orbuilding interiors.

Unfortunately, low-E coatings often do not block significant amounts ofultraviolet (UV) radiation. In other words, low-E coatings typicallyprovide only moderate or negligible UV protection, since the materialsused in the layer stacks are transparent for short wavelengths (e.g.,below 400 nm). In particular, materials used in such layer stacks suchas tin oxide and titanium oxide cannot provide adequate UV protectiongiven the small thicknesses of such materials required for low-Ecoatings. Thus, even with such coatings are provided on windows such asIG windows or vehicle windows, significant amounts of UV radiation makesits way through the window and into the building or vehicle. UVradiation tends to damage furniture and other elements inside ofbuildings or vehicles.

Materials such as vanadium oxide and cerium oxide absorb significantamounts of UV radiation. However, while such materials are characterizedby a very steep onset of absorption for UV radiation, the onset ofradiation absorption occurs in significant part in the visible part ofthe spectrum thereby leading to a significant distortion of colors whenlook through such a coating (e.g., a yellow shift). Accordingly, viewingcharacteristics tend to be degraded when layers of such materials areused.

There also exists a need in the art for improved chemical stability(chemical durability) and heat stability (stability upon heat treatmentsuch as thermal tempering).

In view of the above, it will be appreciated that there exists a need inthe art for a coated article including a low-E coating which is capableof blocking at some UV radiation in an efficient manner. Certain exampleembodiments of this invention relate to a coated article which permitssignificant UV absorption properties to be achieved.

In certain example embodiments of this invention, it has surprisinglybeen found that the provision of a layer consisting essentially of, orcomprising, zirconium oxide (e.g., ZrO₂), zirconium oxynitride, orzirconium silicon oxynitride (e.g., ZrSiO_(x)N_(y)) unexpectedlyimproves blocking (reflecting and/or absorption) of UV radiation in amanner which does not significantly degrade other optical properties ofa coated article such as visible transmission and/or color.Surprisingly, when a layer comprising zirconium oxide or zirconiumsilicon oxynitride is provided as the uppermost or overcoat layer of thecoated article (e.g., over a silicon nitride based layer), this resultsin improved chemical and heat stability in certain example embodiments.

In certain example embodiments of this invention, a layer of zirconiumoxide or zirconium silicon oxynitride may be tuned in a manner so as toachieve a desired amount of UV blocking and/or absorption, as well asimproved durability. It has been found that zirconium oxide or zirconiumsilicon oxynitride has optical constants (n and k) which allowadjustment of the onset of absorption by varying oxygen content of thelayer for example. Moreover, it has been found that zirconium oxide,zirconium oxynitride, or zirconium silicon oxynitride has a refractiveindex (n) in a range which is very adaptable to low-E coatings, so thatsuch layer(s) may be used in low-E coatings without significantlychanging the visible appearance of the coated article or certainperformance data. Thus, in certain example embodiments of thisinvention, the absorption edge of the curve defined by a layer ofzirconium oxide or zirconium silicon oxynitride can be adjusted bychanging the oxygen content thereof, which may be done for example byadjusting the amount of oxygen introduced into the sputtering chamber(s)during reactive sputter-deposition of the layer. In particular, forexample, as oxygen content of the layer increases, the absorption edgeof the curve defined by the layer of zirconium oxide or zirconiumsilicon oxynitride moves toward lower wavelengths away from certainvisible wavelengths. Thus, in certain example embodiments, a balancingor tuning can be performed so as to achieve a desired balance betweenvisible transmission and UV absorption.

In certain example embodiments of this invention, there is provided acoated article including a coating supported by a glass substrate, thecoating comprising, in this order from the glass substrate outwardly: afirst dielectric layer; a first contact layer; an infrared (IR)reflecting layer comprising silver located on the substrate over atleast and contacting the first contact layer; a second contact layercomprising Ni and/or Cr located over and contacting the IR reflectinglayer; a second dielectric layer comprising silicon nitride located overthe second contact layer; and an overcoat dielectric layer comprises oneor more of zirconium oxide, zirconium oxynitride, and/or zirconiumsilicon oxynitride located over and contacting the second dielectriclayer comprising silicon nitride.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a coated article according to anexample embodiment of this invention.

FIG. 2 is a cross sectional view of a coated article according toanother example embodiment of this invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

Referring now to the drawings in which like reference numerals indicatelike parts throughout the several views.

Coated articles herein may be used in coated article applications suchas monolithic windows, IG window units, vehicle windows, and/or anyother suitable application that includes single or multiple substratessuch as glass substrates.

Certain embodiments of this invention relate to a coated article whichincludes at least one glass substrate supporting a coating. The coatingtypically has at least one infrared (IR) reflecting layer which reflectsand/or blocks at least some IR radiation. The IR reflecting layer(s) maybe of a material such as silver, gold, NiCr or the like in differentembodiments of this invention. Often, an IR reflecting layer issandwiched between at least first and second dielectric layers of thecoating. In certain example embodiments of this invention, it hassurprisingly been found that the provision of a layer 16 consistingessentially of, or comprising, zirconium oxide or zirconium siliconoxynitride (e.g., ZrSiO_(x)N_(y)) as a dielectric layer(s) of such acoating unexpectedly improves blocking (reflecting and/or absorption) ofUV radiation in a manner which does not significantly degrade otheroptical properties of a coated article such as visible transmissionand/or color. One or more such zirconium oxide or zirconium siliconoxynitride layers may be provided in a given coating in differentembodiments of this invention. Moreover, such zirconium oxide orzirconium silicon oxynitride layer(s) may be provided in any type ofsolar control or low-E (low-emissivity, or low-emittance) coating indifferent embodiments of this invention (e.g., as an overcoat), and thespecific low-E coatings described herein are for purposes of exampleonly unless recited in the claim(s). When a layer comprising zirconiumoxide or zirconium silicon oxynitride is provided as the uppermost orovercoat layer of the coated article (e.g., over a silicon nitride basedlayer), this results in improved chemical and heat stability in certainexample embodiments. The use of a layer of zirconium oxide or zirconiumsilicon oxynitride in this respect (e.g., as an overcoat layer) hassurprisingly been found to improve chemical stability and heatstability, and has also been found to be stable during sputteringprocessing.

In certain example embodiments of this invention, the oxygen content ofthe zirconium oxynitride or zirconium silicon oxynitride layer(s) 16(e.g., see FIG. 1) is adjusted so that the zirconium silicon oxynitrideinclusive layer has an index of refraction (n) (at a wavelength of 550nm) of from about 1.6 to 2.8, more preferably from about 1.7 to 2.5, andeven more preferably from about 1.8 to 2.4. Moreover, the oxygen contentof the zirconium silicon oxynitride layer(s) 16 is adjusted so that thezirconium silicon oxynitride inclusive layer has an extinctioncoefficient (k) (at a wavelength of 550 nm) of no greater than about2.3, more preferably no greater than about 2.0, even more preferably nogreater than about 1.8. Tuning of the oxygen content of the zirconiumsilicon oxynitride 16 in such a manner has been found to permit good UVabsorption to be achieved in combination with not significantlyadversely affecting visible characteristics of the coated article.Moreover, tuning of the oxygen content in such a manner causes thezirconium silicon oxynitride to have a refractive index which is closeto that of certain layers often used in low-E coatings such as oxides ofTi, Sn, Zn and/or the like. As an example, the absorption edge of azirconium silicon oxynitride layer 16 can be moved over a largewavelength range and may be positioned above, below, or substantially ona ZnO reference edge merely by changing the oxidation level of the layerthereby permitting it to substantially match ZnO from an opticalperspective in certain example instances. Thus, such zirconium siliconoxynitride may replace part of all of such layers in low-E coatings incertain situations without significantly adversely affecting visiblecharacteristics of the coated article. The achievable UV protection islargely dependent on the position of the absorption edge and the layerthickness required by the optical properties of the overall coating.

Moreover, in forming the zirconium silicon oxynitride layer(s) 16according to certain example embodiments of this invention (e.g., viareactive sputtering), the ratio of nitrogen/oxygen (e.g., N₂/O₂) gasused in the sputter chamber is no greater than about 25, more preferablyno greater than about 18, more preferably no greater than about 10. Incertain example embodiments of this invention, the ratio ofnitrogen/oxygen (e.g., N₂/O₂) gas used in the sputter chamber in forminga layer 16 of or including zirconium silicon oxynitride is from about 1to 25, more preferably from about 2 to 18, and sometimes from about 2 to10. Additionally, according to certain example embodiments of thisinvention, a zirconium silicon oxynitride layer 16 is characterized by aratio of nitrogen to oxygen (atomic percent) therein of from about 1 to25, more preferably from about 2 to 18, and sometimes from about 2 to10. Of course, other gases such as Ar may also be used in the sputteringchamber along with oxygen and nitrogen when sputter depositing a layerof zirconium silicon oxynitride. In certain example embodiments, theamount of Ar gas used in sputtering is greater than the amount of oxygenbut less than the amount of nitrogen used in forming a layer ofzirconium oxynitride or zirconium silicon oxynitride 16. For example, incertain example embodiments, the gas ratio used in sputter depositing alayer of zirconium silicon oxynitride is 40 ml Ar, 55 ml N₂ and 10 mlO₂.

Moreover, in certain example embodiments of this invention, the peak ofthe refractive index curve (e.g., see FIG. 4) for a layer of zirconiumoxide or zirconium silicon oxynitride is at a wavelength shorter thanabout 400 nm, more preferably shorter than about 375 nm, and sometimesshorter than about 350 nm, and even sometimes shorter than about 300 nm.In addition to the aforesaid advantageous optical properties, zirconiumoxide or zirconium silicon oxynitride layers according to differentembodiments of this invention realize good mechanical and chemicaldurability. Thus, such layers may be suitable for use in base coats orovercoats in solar control and/or low-E coatings for example.

In certain example embodiments of this invention, the Zr/Si ratio(atomic percent) in an example zirconium oxynitride or zirconium siliconoxynitride layer may be from about 0.25 to 5.0, more preferably fromabout 0.5 to 4, even more preferably from about 0.75 to 3.0, and stillmore preferably from about 1.0 to 2.0, and most preferably from about1.25 to 1.75. Thus, in certain example embodiments of this inventionthere is more Zr than Si in a layer of or including zirconium siliconoxynitride in terms of atomic percent. Moreover, in certain exampleembodiments, an example zirconium silicon oxynitride layer may be fromabout 20 to 400 Å thick, more preferably from about 40 to 300 Å thick,and even more preferably from about 50 to 250 Å thick. In certainexample embodiments, the layer 16 of or including zirconium siliconoxynitride may be of or include from about 20-45% (more preferably25-40%, most preferably from about 30-36%, or 33%) Si, from about 40-65%(more preferably 45-63%, most preferably from about 50-59%, or 54%) Zr,with the rest being made up of optional dopant such as Al and/or Y₂O₃.An example is about 60% Zr and about 40% Si, in layer 16 in the FIG. 1embodiment. In certain example embodiments, the layer 16 (in either theFIG. 1 or FIG. 2 embodiment) includes from about 2-8% (more preferablyfrom about 3-7%, or about 5%) Al, and from about 2-12% (more preferablyfrom about 4-10%, or about 6-8%) Y₂O₃. It is noted that in the FIG. 1embodiment, the layer 16 may instead be of zirconium nitride, zirconiumoxide, or zirconium oxynitride.

As explained above, zirconium oxide or zirconium silicon oxynitridelayers according to different example embodiments of this invention maybe used in various locations in solar control coatings. The coatingsdescribed below are provided for purposes of example.

FIGS. 1-2 are cross sectional view of a coated article according to anexample embodiment of this invention. The coated article includes glasssubstrate 1 (e.g., clear, green, bronze, or blue-green glass substratefrom about 1.0 to 10.0 mm thick, more preferably from about 1.0 mm to6.0 mm thick), and a multi-layer coating (or layer system) provided onthe substrate either directly or indirectly. As shown in FIG. 1, thecoating 25 comprises dielectric layer 20, contact layer 8 of orincluding NiCr or an oxide of nickel chrome (e.g., NiCr or NiCrO_(x)),IR reflecting layer 9 including or of silver, gold, or the like, uppercontact layer 10 of or including NiCr or an oxide of nickel chrome(e.g., NiCr or NiCrO_(x)), dielectric layer 15 (e.g., of or includingsilicon nitride), and dielectric layer 16 of or including a materialsuch as zirconium oxide, zirconium oxynitride, or zirconium siliconoxynitride which may in certain example instances be a protectiveovercoat. Certain characteristics of the layer 16 are discussed abovewhen the layer 16 is of or including zirconium silicon oxynitride. Thezirconium oxide, zirconium oxynitride, or zirconium silicon oxynitridelayer 16 may be doped (e.g., with Al or the like) in certain exampleembodiments of this invention. Other layers and/or materials may also beprovided in certain example embodiments of this invention, and it isalso possible that certain layers may be removed or split in certainexample instances.

Infrared (IR) reflecting layer 9 is preferably substantially or entirelymetallic and/or conductive, and may comprise or consist essentially ofsilver (Ag), gold, or any other suitable IR reflecting material. IRreflecting layer 9 helps allow the coating to have low-E and/or goodsolar control characteristics such as low emittance, low sheetresistance, and so forth. The IR reflecting layer 9 may, however, beslightly oxidized in certain embodiments of this invention.

The upper and lower contact layers 8 and 10 may be of or include anoxide of Ni and/or Cr. In certain example embodiments, upper and lowercontact layers 8, 10 may be of or include nickel (Ni), chromium/chrome(Cr), a nickel alloy such as nickel chrome (NiCr), Haynes alloy, anoxide of any of these, or other suitable material(s). For example, oneof these layers may be of or include zinc oxide instead of NiCr. The useof, for example, NiCr in these layers allows durability to be improvedin certain example instances, and the provided thicknesses permit lowΔE* values to be achieved. Contact layers 8 and 10 (e.g., of orincluding Ni and/or Cr) may or may not be continuous in differentembodiments of this invention across the entire IR reflecting layer. Incertain example embodiments, one or both of the NiCr layers 8, 10includes from about 70-81% Ni, from about 15-19% Cr, from about 3-6% Al,and possibly from about 0-4% (or 1-4%) Fe. An example is 76.5% Ni, 17%Cr, 4.3% Al, and optionally about 2.2% Fe, for one or both of layers 8,10.

Dielectric layers 15 and 20 may be of or include silicon nitride (e.g.,Si₃N₄) or any other suitable material in certain example embodiments ofthis invention such as silicon oxynitride. These layers are provided fordurability purposes, and to protect the underlying layers, and also forantireflective purposes. In certain example embodiments, layers 15 and20 each may have an index of refraction (n) of from about 1.9 to 2.2,more preferably from about 1.95 to 2.05.

It has been found that the provision of an overcoat layer 16 of orincluding zirconium oxide (e.g., see FIG. 2) can reduce and/or eliminatethermal stability problems. In particular, in certain exampleembodiments of this invention, the use of a zirconium oxide inclusiveovercoat layer 16 in combination with the silicon nitride based layer 15and contact layer 10 can result in a coated article which can besignificantly heat treated (e.g., thermally tempered) without sufferingfrom significant mottling damage or other damage from heat treatment(e.g., the coated article can realize acceptable visible transmission,a* and/or b* values following heat treatment such as thermal tempering).In certain example embodiments, the index “n” of the zirconium oxidelayer 16 is from about 2.1 to 2.25, more preferably about 2.16 (at 550nm).

It has been found that by using zirconium oxide or zirconium siliconoxynitride as a top or overcoat layer 16 with silicon nitride 15underneath the same as shown in FIGS. 1-2, the coated article realizes ahigher light transmission and a significant drop in sheetresistance—both of which are unexpected improvements/results. UnexpectedUV advantages are also realized as discussed above, due to the use ofzirconium oxide or zirconium silicon oxynitride. This embodiment may beheat treated (thermally tempered with the coating thereon) in certainexample embodiments of this invention.

Other layer(s) below or above the illustrated coating 25 may also beprovided. Thus, while the layer system or coating is “on” or “supportedby” substrate 1 (directly or indirectly), other layer(s) may be providedtherebetween. Thus, for example, the coating of FIG. 1 may be considered“on” and “supported by” the substrate 1 even if other layer(s) areprovided between layer 3 and substrate 1. Moreover, certain layers ofthe illustrated coating may be removed in certain embodiments, whileothers may be added between the various layers or the various layer(s)may be split with other layer(s) added between the split sections inother embodiments of this invention without departing from the overallspirit of certain embodiments of this invention.

The value(s) ΔE* is important in determining whether or not there isthermal stability, matchability, or substantial color matchability uponHT, in the context of certain embodiments of this invention (i.e., theterm ΔE* is important in determining color stability upon HT). Colorherein is described by reference to the conventional a*, b* values. Forexample, the term Δa* is indicative of how much color value a* changesdue to HT. The term ΔE* (and ΔE) is well understood in the art. Thedefinition of the term ΔE* may be found, for example, in WO 02/090281and/or U.S. Pat. No. 6,475,626, the disclosures of which are herebyincorporated herein by reference. In particular, ΔE* corresponds to theCIE LAB Scale L*, a*, b*, and is represented by:

ΔE*={(ΔL*)²+(Δa*)²+(Δb*)²}^(1/2)  (1)

where:

ΔL*=L* ₁ −L* _(o)  (2)

Δa*=a* ₁ −a* _(o)  (³)

Δb*=b* ₁ −b* _(o)  (4)

Above, the subscript “o” represents the coating (or coated article)before heat treatment and the subscript “1” represents the coating (orcoated article) after heat treatment; and the numbers employed (e.g.,a*, b*, L*) are those calculated by the aforesaid (CIE LAB 1976) L*, a*,b* coordinate technique. In a similar manner, ΔE may be calculated usingequation (1) by replacing a*, b*, L* with Hunter Lab values ah, bh, Lh.Also within the scope of this invention and the quantification of ΔE*are the equivalent numbers if converted to those calculated by any othertechnique employing the same concept of ΔE* as defined above.

It has been found that thinning the NiCr layers 8 and 10 results in good(lower) ΔE* values compared to a situation where layers 8, 10 are notthinned. In certain example embodiments, the upper NiCr based layer 10is thinner than the lower NiCr based layer 8. In certain exampleembodiments of this invention, NiCr based layers 8, 10 are thinned andthe resulting coated article due to heat treatment has a ΔE* value(glass side reflective) of no more than 3.0, more preferably no morethan 2.5, even more preferably no more than 2.0 and possibly no morethan 1.5.

While various thicknesses may be used in different embodiments of thisinvention, example thicknesses and materials for the respective layerson the glass substrate 1 in the FIG. 1-2 embodiments are as follows,from the glass substrate outwardly:

TABLE 1 (Example Materials/Thicknesses) More Layer Range ({acute over(Å)}) Preferred ({acute over (Å)}) Example (Å) Si₃N₄ (layer 20) 150-700{acute over (Å)} 200-600 {acute over (Å)} 380 Å NiCr (layer 8) <=12{acute over (Å)} <=10 {acute over (Å)} 7-8 Å Ag (layer 9) 30-170 {acuteover (Å)} 40-110 {acute over (Å)} 67 Å NiCr (layer 10) <=11 {acute over(Å)} <=9 {acute over (Å)} 6-8 Å Si₃N₄ (layer 15) 150-700 {acute over(Å)} 200-600 {acute over (Å)} 365 Å ZrO₂ or ZrSiO_(x)N_(y) 40-400 {acuteover (Å)} 100-200 Å 150 Å (layer 16)

In certain example embodiments of this invention, coated articles hereinmay have the following low-E (low emissivity), solar and/or opticalcharacteristics set forth in Table 2 when measured monolithically.

TABLE 2 Low-E/Solar Characteristics (Monolithic) Characteristic GeneralMore Preferred Most Preferred R_(s) (ohms/sq.): <=20.0 <=15.0 <=10.0T_(vis) (%): >=50 >=60 >=70 or 75

Moreover, coated articles including coatings according to certainexample embodiments of this invention have the following opticalcharacteristics (e.g., when the coating(s) is provided on a clear sodalime silica glass substrate 1 from 1 to 10 mm thick, preferably about 4mm thick). In Table 3, all parameters are measured monolithically(before and/or after heat treatment).

TABLE 3 Example Optical Characteristics (Monolithic) CharacteristicGeneral More Preferred T_(vis) (or TY)(Ill. C, 2 deg.): >=60% >=70% or75% a*_(t) (Ill. C, 2°): −6 to +6 −3 to 0   b*_(t) (Ill. C, 2°):   −10to +10.0 −4 to 0   L*_(t): >=89 >=90 R_(f)Y (Ill. C, 2 deg.): <=10% <=6%a*_(f) (Ill. C, 2°): −5 to +5 −3 to +2 b*_(f) (Ill. C, 2°): −14.0 to+10.0 −10.0 to +5   L*_(f): 22-30 24-27 R_(g)Y (Ill. C, 2 deg.): <=11%<=7% a*_(g) (Ill. C, 2°): −7 to +7 −2 to +7 b*_(g) (Ill. C, 2°): −10.0to +10.0 −2.0 to +7   L*_(g): 23-38 25-37

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1-10. (canceled)
 11. A coated article including a coating supported by aglass substrate, the coating comprising from the glass substrateoutwardly: a first dielectric layer comprising silicon nitride; a firstcontact layer; an infrared (IR) reflecting layer comprising silverlocated on the substrate over at least and contacting the first contactlayer; a second contact layer located over and contacting the IRreflecting layer, the second contact layer having a thickness of lessthan or equal to 11 angstroms; a second dielectric layer comprisingsilicon nitride located over and contacting the second contact layer;and an overcoat dielectric layer comprising one or more of zirconiumoxynitride and zirconium silicon oxynitride located over and contactingthe second dielectric layer comprising silicon nitride, and wherein theovercoat dielectric layer is doped with Y.
 12. The coated article ofclaim 11, wherein the first dielectric layer comprising silicon nitrideis in direct contact with the glass substrate.
 13. The coated article ofclaim 11, wherein the overcoat layer comprises zirconium siliconoxynitride.
 14. The coated article of claim 11, wherein the coatedarticle has a sheet resistance (R_(S)) of no greater than about 15ohms/square and a visible transmission of at least about 70%.
 15. Thecoated article of claim 11, wherein the overcoat layer compriseszirconium oxynitride.
 16. The coated article of claim 11, wherein thefirst contact layer comprises Ni and Cr, and has a thickness of 7-8angstroms.
 17. The coated article of claim 11, wherein the overcoatlayer is doped with from about 2-12% Y₂O₃.